Add missing +/-/' ' on diff views

The diff formatter forgot to include the prefix character at the
start of each line in the region. Add the prefix before the rest
of the line text.

Bug: http://code.google.com/p/gitiles/issues/detail?id=15
Change-Id: If8e45c8c2ae2c2b592addd1dee94c2216b2388a5
1 file changed